Rescued shitzu.. Not sure if I spelled that right.

Question
Okay so I rescued a shitzu yesterday.  She is well trained and house borken and so calm with kids and other animals.  She was not taken care of and the people had very little info.  They said the vet checked her and said she was between 2 and 3 years old but looked to have been over breed.  Today I bathed her and noticed she was missing teeth and as I was doing so another fell out into my hand.  Do you think it's possible the over breeding her would cause teeth problems or they were lying about the age.  She is spunky and healthy looking so I wouldn't think she is too old.  So sorry if this is considered medical she will be taken to the vet asap.  We are just tryen to decide weather or not we were told the truth.  Any advice would be great.  When I googled this it popped up a story about the same kind of dog with a tooth lose as well. So I figured this was worth a shot.  
Thanks, Amanda

Answer
Sounds like she may have periodontal disease,and even very young dogs can lose teeth from it,it is caused by neglect and not brushing the teeth ect because she has this problem,she may need to be put under and have her teeth scaled by your vet,to prevent more teeth from falling out

Also toy breeds are prone to dental problems to begin with,so being neglected will make things worse-your vet will show you how to brush your dogs teeth,and only use dog tooth paste,as human tooth paste will make the dog sick